Height and weight at menarche were estimated by interpolation of longitudinal growth data for 181 girls. Mean weight at menarche, about 48 kg, does not change as menarcheal age increases, whereas mean height increases significantly. Early and late menarcheal girls gain the same amount of height, about 22 cm, and the same amount of weight, about 17 kg, in the interval from the initiation of the adolescent spurt to menarche, though late maturers grow at slower rates during the spurt, including the year of menarche. A hypothesis of a direct relation between a critical weight and menarche is proposed. Such an interaction would explain the delaying effect of malnutrition on menarche and the secular trend to an earlier menarche.